1. Field of the Invention
The present invention relates to devices and techniques for securing bone segments across a fracture site, and more particularly relates to a bone stapling method and apparatus for achieving compression between segments.
2. Description of the Prior Art
In treating a bone fracture it is common practice to fasten one bone segment to the other so as to stabilize and immobilize them for the duration of the bone consolidation process. Thus there is the technique of internal fixation or direct mechanical fastening of the bone segments.
Traditionally, fixation has been accomplished by variety of apparatus and techniques, the more common involving the use of metallic fastening devices such as screws, connector plates (secured to the bone by screws), pins and clips. These methods invariably involve the drilling of screw holes in the bone and the use of related equipment such as drill hole templates. Conventional U-shaped clips have also been used, the clip legs being installed one each in holes in the opposing bone segments. The rigid structure of such clips, like the other fixation devices mentioned above, provide rigid immobilization of the fracture zone. Such devices also served to maintain the distance between segments, which was found however, among other things, to hinder compression induced by contractions of skeletal muscles in some cases, and prevent the establishment of compressive force between the bone segments which is favorable to bone consolidation or knitting. In this regard the concept of creating dynamic compressive force across an osteotomy or bone fracture site has become well recognized as a technique to promote primary bone healing, i.e. consolidation that is faster and of better quality.
Thus there has evolved a number of fastening devices such as clips and the like, designed to deliver compression. Accordingly in U.S. Pat. No. 3,939,294 there is provided a clasp or clip of spring material having a pair of spaced-apart, inwardly inclined legs connected by a Z-shaped upper portion. Sloped holes are drilled in adjoining bone segments and tools are used to manipulate and install one leg, and then the other leg is pulled toward the other hole, spreading the Z-shaped elastic portion, and then inserted in the other hole. Unfortunately this method requires the drilling of specially sloped holes, involves multiple steps and is time-consuming, and like the conventional rigid fastening techniques, requires relatively large surgical opening. Also, the manual installation of the clip using hemostats and the like is difficult, requires meticulous skill and handling.
In U.S. Pat. No. 4,838,254 the legs of a pair of metallic clips are inserted in pairs of specially angled bores in respective opposing bone segments The exposed tops of the two installed clips then serve as fastening heads for a spring that is connected between the clips.
In U.S. Pat. No. 4,841,960 the disclosed xe2x80x9ccompressionxe2x80x9d clip is essentially a clip with opposing legs that are installed in pre-drilled holes and features a crimpable web that joins the top ends of the legs. A crimping tool is used to crimp the web in an effort to set up compression between the embedded legs.
U.S. Pat. No. 4,852,558 also requires manual installation of separate legs in pre-drilled holes, the tops of the install legs then being interconnected with a ratchet mechanism which must be operated to draw the legs together. This design appears inherently limited regarding adjustability and maintenance of constant pressure. In U.S. Pat. No. 5,660,188 the two legs of a clip must also be installed in pre-drilled holes. The clip has a bridge of two side-by-side crimpable elements, and the jaws of a crimping tool must be used on the embedded clip to deformingly spread apart these elements, causing the legs to draw to each other. The foregoing techniques involving crimpable clips all appear to be imprecise in setting up suitable compressive forces, require hole drilling and related problems, and do not lend themselves to minimizing the size of the surgical opening.
In view of the limitations of the afore-mentioned methods, stapling has been looked to as a potentially quick and effective way for fastening bone segments, and as a way to produce compression. Thus in U.S. Pat. Nos. 5,053,038 and 5,662,655xe2x80x9ccompressionxe2x80x9d staples are applied to the bone by a powered stapler. These staples have legs shaped with beveled ends and/or have divergent legs that will be forced apart from each other during implantation, which flexes springy upper parts of the legs thereby tending to set up compression. Unfortunately there is concern for trauma to the bone due to driving of the compound-shaped legs into the bone mass, and there is little apparent precision in establishing the desired compressive forces.
In view of the foregoing it is a general object of the present invention to provide an improved method and for interosseous fastening.
A more particular object is to provide quick and simple, yet effective method for fastening bone segments with compressive force between opposing bone ends.
Another object to provide such a method that minimizes the size of the required surgical opening and associated trauma.
A further object to provide a method of bone stapling that minimizes trauma to the bone tissue during implantation of the staple legs.
Yet another object is to provide a method for stapling that maximizes the capability of establishing a dynamic compression level that is optimal for enhanced osseous healing.
A still further object is to provide simple, effective bone fixation technique that is relatively easy to learn and practice.
Another object is to provide for compression fixation in applications where other techniques would not work or would not deliver compression. For example, conventional fastening techniques for handling a xe2x80x98Jonesxe2x80x99 fracture, i.e. one that is transverse to the longitudinal extent of the bone segment, is difficult to address using conventional fastening techniques, however the present invention is particularly suitable to provide fastening for such fractures.
Still another object is to provide stapling apparatus and method in which there is enhanced selection capability regarding the level of the compressive forces to be imparted.
There are a number of advantages in exterior bone fixation techniques, where surgical incisions are not required and fasteners are applied through the skin, and thus it is yet another object of the invention to provide a bone stapling method that lends itself well to exterior bone fixation.
These and other objects of the present invention are achievable by way of the present invention of a bone stapling method and apparatus that uses a generally U-shaped staple having pair of spaced apart legs with sharp free ends and proximal ends interconnected by bridge that has at least one resilient curved portion, whereby spreading apart of the parallel legs lessens the curvature of the curved portions which brings the staple to a tensioned configuration in which one leg is resiliently urged towards the other. In a preferred embodiment it is seen that the bridge portion comprises a single bowed spring element, the curvature of which lies in a plane normal to the axes of the staple legs.
The novel fastening method involves first positioning the fractured ends of a first and a second bone segment in proximate, face-to-face relationship. The next step involves spreading apart the staple legs by a certain amount and holding the staple in the resultant tensioned configuration. The extent to which the staple legs are separated can be varied in one preferred embodiment of the invention, the induced compressive forces between the legs being proportional to the amount of displacement of the legs as the bowed portion is moved through range of motion in which elastic behavior is exhibited. In this regard it should be evident that herein lies one of the advantages of the present invention, i.e. the capability of selecting the optimal compressive force for an application by spreading apart the staple legs by a predetermined amount.
Next, as the staple is held in its tensioned configuration, it is positioned with it sharp ends forward and aligned respectively with surfaces of one bone segments and the other. Finally the positioned staple, while maintained in its tensioned configuration, is driven into the bone by percussive force, such quick application being provided by a conventional air-powered striker of a stapler according to the present invention, or by a manually stuck staple applicator according to the invention. The embedded staple legs will cause the opposing bone faces to be pressed into each other with a predetermined amount of force.
Such stapling method lends itself advantageously to a staple with a relatively narrow profile, wherein apparatus according to the present invention include a staple applicator having within its housing means for supporting the staple and guiding its movement with legs pointed ends forwardly disposed, and adapted to receive the staple in its initial un-tensioned configuration engaging its legs and spreading them apart by certain amount and holding the staple in its tensioned configuration adjacent the front end of the housing, for ejection therefrom. One embodiment. of several uses opposing first and second grooves for engaging the staple legs and means for adjustably moving one groove from the other. Another embodiment employs grooves that diverge to spread the staple legs as a staple is advanced there-along. Ejection means mounted for longitudinal movement in the housing has a front end adapted to strike the rear of the tensioned staple with percussive force which is provided by air power or electrical power in preferred embodiments.
The invention also includes a staple applicator that is adapted for being manually driven. Another related bone stapling method for compressively securing adjoining bone segments uses a resilient metallic staple that has legs with an initial convergent configuration with respect to each other, and the legs are resiliently extendible into parallel relationship, in which configuration a predetermined amount of spring force will urge the legs towards their initial convergent orientation. This method includes holding the normally convergent staple in its legs-parallel configuration, positioning the so-tensioned staple with its sharp ends aligned respectively with adjacent bone surfaces; and then driving and embedding the legs of the tensioned staple in the bone segments and releasing the embedded staple, whereby the bone segments are joined, and opposing surfaces of the bone segments are caused to be pressed into engagement with each other with a certain amount of compressive force.
An applicator or tool for such a staple includes staple-engaging means on the front end of the applicator body. Opposing jaws support the staple in a pointed-ends forward position against lateral and rearward movement, and engage inside surfaces of the convergent legs, the jaws being adapted for adjustable movement apart to cause the legs to rotate to a generally parallel orientation. Thus supported on the front end of the tool, the staple can be aligned with the bone segments, and the rear end of the tool stuck with a percussive force to cause the staple legs to be embedded into the bone segments.
Another applicator according to the present invention has a trigger-controlled air-powered staple-driving mechanism, and has a staple feeding mechanism including ramp means that is shaped to receive and support a staple in its initial configuration on one end of said ramp means, the configuration of the ramp means gradually changing to a shape that will hold the staple with its legs generally parallel with each other. Thus the staple can be slidably pushed along the ramp means in a lateral direction, i.e. normal to the plane in which the staple legs and bridge portion lie, to bring it to a terminal position along the ramp means, in which position the rear of the tensioned staple can be struck by the front end of a powered striker.